"When compared with death rates in the general population of England in 1998, there was no evidence for a higher incidence of mortality in this group."

Cardiologist Dr Mark Adams of Sydney's Royal Prince Alfred Hospital said that the study supports current guidelines for prescribing Viagra.

"As long as people do not have a problem with low blood pressure and are not taking nitrate medications, then the increase in risk is small," he said.

Viagra potentiates the vasodilating effects of nitrate medications.

"The findings are an extra bit of reassurance on what we thought before," he said. "However the study has its limitations."

Users of Viagra (sildenafil) were identified from NHS prescriptions in England and sent questionnaires via their prescribing GPs about five months after the first prescription, requesting details of events after the drug had been prescribed.

Dr Adams points out that out of 9,748 questionnaires sent out only 5,950 were returned.

"This is a very low return rate," he said. "There is no indication in the study why so many surveys didn't come back. Maybe the patients were dead."

The authors themselves state that although their findings were reassuring, further evidence was needed for confirmation.

The journal discloses that two of the authors have received financial support from Pfizer to attend conferences overseas.